Dealing with resistant pigweeds in Arkansas' Clay County

Arkansas’ Clay County is largely known for its excellent cotton. However, if not for the recent collective effort of producers, it could easily be known for its resistant pigweed.

Glyphosate-resistant weeds are not a novelty to area farmers. Before major populations of resistant Palmer amaranth showed up, they had to deal with resistant horseweed.

“We actually learned how to deal with horseweed using dicamba and Roundup Ready crops,” says Andy Vangilder, Clay County Extension staff chair. “We’ve done a good job on horseweed.”

Then, three or four years ago, farmers began finding Palmer amaranth that looked to be resistant. In 2009, Vangilder sent samples off for evaluation. They came back at resistance levels of 7 to 10 percent.

In the fall of 2010, “big clusters of pigweed – car-size patches -- showed up in areas we’d sprayed and taken care of properly. I sampled three fields and those numbers came back at 55-, 85- and 100 percent resistant. At that point, we knew pigweed was about to blow up and cause our fields major problems.”

Vangilder began talking to Ken Smith, University of Arkansas weed scientist. Following Smith’s suggestions, “we had a meeting with our agri-dealers in the area. We said ‘this is what’s happening and this is what it will take to control these resistant weeds.’ They said ‘if you’ll put this on paper, give us your recommendations, we’ll do it.’ So, we put together a fact sheet for Clay County and our dealers brought in the needed products. They made sure our farmers had the chemicals.”

Several of the leading farmers in the county then “started to talk about doing more, going with ‘zero tolerance’ of pigweeds. They began spraying their turnrows, chopping and keeping things really clean. More folks began doing the same and we’ve continued it through this season.”

Farmers, watching the encroachment of hard-to-kill pigweeds, were anxious “to get ahead before it got too bad,” says Vangilder. “And we still have grown-up fields that folks haven’t paid enough attention to. But drive around this northeast Arkansas area and I don’t think there’s anywhere cleaner in the state.”

During a recent tour of the area, “Smith was impressed with what the farmers here have been doing. It isn’t just the fields – they want it all clean. They got hooded sprayers that won’t drift as much.”

As for the areas in the county where pigweeds are still evident, “you have to understand it isn’t due to laziness. One of the problems, of course, is we flooded so badly up here early in the season. The corn was behind, planting of crops dragged. That meant there was much less time to spray these resistant pigweeds.”’

However, Vangilder says such circumstances don’t absolve the need to keep one’s property pigweed-free. “Certainly seeing your neighbor’s turnrow is clear while yours is grown up plays a role in everyone picking up the pace. There’s some subtle pressure there. Everyone is starting to improve their efforts and I think 2012 will even be better.”

No let-up

How did resistant pigweeds progress across Clay County?

“They seemed to move in from the east,” says Vangilder. “But this area may have developed our own resistant pigweeds. I don’t think that’s unusual.

“I think part of the problem is we sprayed too many pigweeds when they were too big. We were able to kill larger pigweed plants for a long time and so we just kept doing the same thing without rotating chemistries.”

Vangilder also saw some big plants “that appeared to have been damaged from the wheels. That happened when the wheel ran over it while spraying. It seemed like a lot of those survived and didn’t get good coverage.”

Pigweed fatigue can set in, admits Vangilder.

“Some farmers have done well all summer in dealing with pigweeds. But, right now, there are a few pigweeds in the field or on the edges that have come up. Those wouldn’t be hard to get but some aren’t doing it. I wish they would.

“Well, you can’t quit. If you leave three or four and the seed scatter with the picker you’re back to square one. Whatever you gained in that summer fight can easily be lost.”

When a combine hits a pigweed, “it’ll show up in the field – right down the row – the next year. If you don’t have a residual down, you’ll see the line where that (parent) pigweed was picked up and seed scattered down the row.”

Lessons learned

Two years ago, if there were 20 pigweeds in a field “you wouldn’t have thought a thing about it,” says Vangilder. “You’d have picked your cotton and thought, ‘well, there are a few pigweeds scattered through here.’But, now, we’ve seen what those 20 can turn into.”

And through their collective clean-up efforts, producers have learned lessons.

“We need to take the information the weed experts deliver to us and use it,” says Mike Morgan, a cotton farmer in Clay County. “Then, hopefully, we won’t see more resistance to other chemicals.

“A lot of our crews, when they started chopping, might chop the weed an inch or two from the ground. Well, that won’t work with a pigweed. Those things will just grow out and then come back up. You really have to chop them flush with the ground, or underground.”

Morgan’s fields are set up to irrigate every other middle. “If you allow a chopped plant to lie (in an irrigated middle) it’ll still seed that area. You have to put them in a dry middle. You cannot believe how tough these plants are. It’s unreal how resilient these pigweeds are. It’s the toughest plant I’ve ever seen.”

Vangilder and Morgan say at first glance it would be a good idea to get the state or municipalities involved in pigweed control. But after careful consideration any such involvement carries a passel of concerns.

“It’s true that these resistant weeds are all up and down the highways, now,” says Morgan. “They mow a couple times a year. But you can cut a pigweed off and it’ll be right back and going to seed in no time.”

A day earlier, Vangilder spoke with a county Extension agent from Tennessee. “The county he works was one of the first that had this problem with resistance. He was interested in what we’re doing and if the state would get involved.

“I told him ‘I don’t know if they will, or not. But my concern is this: what we’re using mostly is Gramoxone plus a residual like Direx. We don’t want to get folks involved that aren’t up to speed on all the issues surrounding resistance.

‘First, does the state have hooded equipment? They’d have to purchase it. Second, it would require trained employees who wouldn’t damage crops in fields near highways. Wind and drift could really cause trouble.”

Highway departments have done damage to crops before by spraying Roundup. “They didn’t mean to do it but you can’t just turn someone loose spraying Johnsongrass without concern for the surrounding crops,” says Vangilder.

Morgan agrees. “If they sprayed Gramoxone in wind out of one of those trucks it would ruin acres and acres. Lawsuits would be filed.”

Even so, says Morgan, “something has to be done with these resistant weeds along highways or county roads. They have to be dealt with. If you allow a pigweed to stay in a ditch, the next year – believe me – they’ll be crawling out of that ditch and into your field. I’ve seen it over and over.”

Tightrope walking

Resistant pigweeds have led to difficult choices for producers.

“One grower who rented ground with pigweeds told me he had to let his main farm slip a little because he was so intent on getting that new land cleaned up,” says Vangilder. “It cost him a little because he didn’t do as well on the main farm as he normally would.”

There is also the financial tightrope farmers are walking.

“Around here, everyone is making at least an effort to control pigweeds,” says Vangilder. “One dryland farmer did some things I’d recommended. Then, we didn’t get any rain and he quit.

“Well, I can’t say I don’t understand – there’s only so much money you can put into a dryland crop. Of course, that will hurt the farms around him with pigweeds migrating quickly. He knows that and feels bad about it. But what’s he supposed to do without the cash flow?

“So, the dryland issue is another issue with these pigweeds. What if you’re non-irrigated and don’t get a rain to activate the pre-emerge herbicides? Economically, where do you stop?”

However, if vigilant pigweed control is financially difficult now, what happens when the price of cotton slips?

Clay County producers, says Vangilder, “are committed and looking to the future. Right now, they’re making less profit on some of their fields by going zero-tolerance but they’re willing to do it.

“One reason for tackling it now is there’s no guarantee of $1-plus cotton in a year, or two. And you can’t do what they’re doing with 52-cent cotton. While they’ve got a chance to clean up and make some money at the same time, they’re on top of it.”

Programs

As for tweaking control programs, Vangilder is unsure about “what else we could do. If there was something else, I believe the farmers would try it.

“Normally, we start in the spring to get rid of the resistant horseweed. And they’ve dealt well with that – it’s not near the problem as it once was.

“Everyone has a different program. But if you don’t have a bad pigweed infestation, the Reflex program may not be something you have to have. But for those that are infested, it can work.”

Producers should be warned about Reflex, though. “We’ve had some bad experiences,” says Vangilder. “You won’t hear me recommend planting cotton then spraying it on the ground. I’m not knocking the product but there’s been too much injury taking that approach.”

Instead, he suggests, spray the Reflex, get a rain and then plant the cotton into it. “That works fine and has been a big help for us.”

Producer Greg Engle says he’s used that “on some of our worst fields. We’ve also sprayed our Direx and that works. We also use Dual and put Cotoran on top of rows.”

“So, they’re using two pre-emergence (products) and then come in with Roundup and Dual twice,” says Vangilder. “Then, they come in with hoods and get the middles with something like Gramoxone, if you’re really careful. And Direx or Valor is used for lay-by.

“It’s a total chemical program along with hand-hoeing -- whatever it takes.”

One thing producers are waiting on is appropriate varieties of LibertyLink cotton for Clay County. Vangilder says “there will be a bunch of producers planting those when they come around.”

Right now, one of the hardest things for Vangilder to impart is to be timely in dealing with pigweeds. “You can’t wait to spray or chop. You can’t push the window and wait until the pigweeds are five inches tall. That’s the wrong thing to do. You cannot be late in dealing with these.”